Method and means for switching on and off the fan wheel of a regulating fan

ABSTRACT

The cooling fan of an internal combustion engine is driven through a temperature-controlled clutch. Slipping of the clutch is held to a minimum by an auxiliary actuating mechanism which automatically moves the clutch into the fully engaged or the fully disengaged position as soon as it has been moved by a thermostat into an intermediate position. Several examples of clutch arrangements are given.

United States Patent 1 1 3,580,229

[72] inventor Michael May [56] References Cited Stuttgart-B918, GermanyUNITED STATES PATENTS gig- 32522 2,078,600 4/1934 Collins 192/522,652,816 9/1953 Dodge 123/4112 2:52:22 ill'iifa m AG 2,881,890 4/1959Welch...... 192/82 g Schw. Main G 2,950,796 8/1960 Becker..... 192/82[32] mm Mar "many 2,998,114 8/1961 Altmann... 192/52 [33] 3,273,68l9/1966 Seifert 123/4112 [31] g 3,323,623 6/1967 Roper 192/58 FOREIGNPATENTS 688,243 6/1964 Canada 123/4112 Primary Examiner-Mark M. NewmanAssistant Examiner-Ronald B. Cox

54 METHOD AND MEANs FOR SWITCHING ON AND AmmeY-LW and Berma" on THE FANWHEEL 0F A REGULATING FAN 8 Chums Drawing Figs ABSTRACT: The cooling fanof an internal combustion en- [52] US. CL l23/4l.l2, gine is driventhrough a temperature-controlled clutch.

192/52, 192/54, 192/83 Slipping of the clutch is held to a minimum by anauxiliary ac- [51] Int. Cl F0lp 7/02, tuating mechanism whichautomatically moves the clutch into F 16d 7/00, F 16d 19/00 the fullyengaged or the fully disengaged position as soon as it [50] Field ofSearch 123/41. l2; has been moved by a thermostat into an intermediateposition.

192/5 2, 54, 83 Several examples of clutch arrangements are given.

Patented May 25, 1971 3,580,229

6 Sheets-Sheet 2 Inventor M 74! May $1M 444 MM Flam/7's Patented May 25,1971 3,580,229

6 Sheets-Sheet 5 Fig. 4

Inventor: fq M4) Patented May 25, 1971 6 Sheets-Sheet 4 Fig.5

Inventor: H/aaa/ May {9 GENT;

Patented May 25, 1971 3,580,229

6 Sheets-Sheet 5 Fig. 6

Inventor fil cda M417 4) GEM/5 Patented May 25, 1911 3,580,229

6 Sheets-Sheet 6 Inventor /aae/ 7' $1M M MW METHOD AND MEANS FORSWITCHING ON AND OFF THE FAN WHEEL OF A REGULATING FAN This inventionrelates to the control of the fan wheel of a regulating fan of aninternal combustion engine, such as a motor vehicle engine, andparticularly to a clutch control mechanism in a regulating fan.

Regulating or automatically controlled fans are known and differ fromordinary internal combustion engine fans in that their fan wheel is notconstantly driven but is only switched on when the engine cooling by thenormal air flow is not sufficient. This affords a number of advantages.For example, the engine reaches its operating temperature substantiallymore quickly. Also, there is a power saving which can amount in the caseof automobiles to a few horsepower and the engine runs more smoothly. Inspite of these advantages, regulating fans have not establishedthemselves generally because they are relatively complicated andexpensive to manufacture. On the other hand, known regulating fans ofsimple design do not operate satisfactorily and reliably. One knownregulating fan is temperature controlled and comprises a drive shaftwhich is driven by the engine via a V-blet and adapted to be coupled tothe fan wheel by a friction coupling. The temperature pickup is a waxthermostat and is exposed to the cooling air heated by the radiator. Acontrol element of the wax thermostat acts on an expanding spring whoseperiphery is provided with a friction lining and adapted to bear againstthe coupling drum of the friction clutch. This regulating fan isadmittedly of simple design; however, the friction clutch slipsconstantly in the critical region because the engaging and disengagingoperations are effected solely by the creeping movement of the controlelement of the wax thermostat. The high slip has both control andoperating disadvantages. Inter alia the cooling effect is impaired andthe clutch lining wears rapidly.

It is proposed according to the invention that the engagement of thefriction coupling associated with the fan wheel from an intennediatefirst coupling state of the friction coupling onwards and thedisengagement from an intermediate second coupling state onwards takeplace automatically without being affected by the temperature to becontrolled until complete engagement and disengagement respectively isachieved, the coupling passing rapidly through the slip range, and thatthe adjustment of the friction coupling necessary to reach the first andsecond coupling states is effected by at least one temperature pickup ofthe temperature-sensing device in dependence upon the temperature to becontrolled.

This method is particularly distinguished by the fact that after thefirst or second coupling state has been reached the clutch is clearlyengaged or disengaged, being in the slip range only for as long as isnecessary for the rapid acceleration of the fan wheel.

The novel method has particular advantages in conjunction withregulating fans whose temperature pickups are so constructed andarranged that they can exert a coupling force directly on the frictionclutch. As already mentioned, in known regulating fans the clutch canslip for long periods. Also, in these regulating fans the width of theslip range increases with increasing drive speed of the fan wheel. Thesedisadvantages are obviated with he novel method of the invention. Thetemperature pickup serves only to control the friction clutch to bringit into a first or second coupling state; when this state is reached thefurther coupling operation proceeds automatically with rapid passagethrough the slip range.

It is known in regulating fans to switch the fan wheel on and off atdifferent values of the temperature to be controlled to prevent rapidreciprocating of the control operation. This problem can also be solvedsimply by the method according to the invention in that the firstcoupling state is reached at a higher value of the temperature to becontrolled than the clutch which comprises a main coupling andpreferably a control coupling associated with the main coupling forcontrolling the latter, then first and second coupling statescorresponding to transition points between the two stable couplingstates of the clutch, one of which is the disengaged and the other theengaged state, and that the temperature-sensing device comprises acontrol device having at least one temperature pickup to sense thetemperature to be controlled and bringing the bistable clutchalternately into the first and second coupling states, said devicepreferably being nonrotatably connected to the drive shaft of theclutch.

Further features of the invention are described hereinafter withreference to the drawings, wherein:

FIG. 1 shows a side elevation partially in section of a regulating fanaccording to a first embodiment of the invention,

FIG. 2 is a perspective view of a detail of FIG. 1,

FIG. 3 shows four positions of the clamping mechanism illustrated inFIGS. 1, 2 and 4 in developed views,

FIG. 4 is a plan view of a detail of FIG. 1,

FIG. 5 is a partial longitudinal section through a fan according to afurther embodiment of the invention, the clutch being disengaged,

FIG. 6 shows a portion of the fan according to FIG. 7 in longitudinalsection with the clutch engaged, and

FIG. 7 is an exploded perspective view of the fan according to FIGS. 7and 8.

In the drawings corresponding parts are provided with the same referencenumerals.

The regulating fan illustrated in FIG. 1 comprises a fan wheel 10, onthe hub 12 of which are arranged a plurality of fan blades 11 shownpartly broken away to simplify the illustrations.

The fan wheel 10 is adapted to be driven by an engine shaft (notillustrated) of a motor vehicle engine (also not shown) via a V-beltdrive, of which a V-belt is indicated at 13 and the driven pulley at 14.For this purpose, the pulley 14 is fixedly arranged on a journal 15which serves as drive shaft for the fan arrangement and which is mountedin a bearing assembly 16 fixedly connected in a manner not illustratedin detail to the engine block, said bearing assembly 16 fixedlyconnected in a manner not illustrated in detail to the engine block,said bearing assembly comprising a ball bearing 17 and a shaft seal 18.The journal 15 comprises a flange 19 to which by means of bolts such as21 the pulley 14 together with one coupling or clutch member 20 of amain coupling or clutch is nonrotatably connected. Furthermore, abushing 22 is fixedly arranged on the journal 15 and a wax thermostat 24serving as temperature pickup and control device is screwed fixedly intothe free slotted end 23 of said bushing.

Said wax thermostat may be of any suitable conventional construction andcomprises a casing 25 whose cylindrical inner chamber 26 contains wax 27having a high thermal expansion coefiicient. Mounted for axialdisplacement in a bearing bore 28 in the end face 29 of the casing 25 isa ram 30 serving as control element.

Spaced in front of the wax thermostat 24 is a radiator not furtherillustrated for cooling the coolant of the motor vehicle engine. Thecooling air flowing through this radiator impinges in the direction ofthe arrow A on the wax thermostat. When the temperature of this airexceeds a predetermined limit, in a manner described in detail hereinafter the fan wheel 10 is switched in by a bistable clutch. As soon asthe cooling air drops below a predetermined lower temperature the fanwheel 10 is switched off again by disengagement of the clutch.

Secured to the hub 12 of the fan wheel 10 is a coupling member 31 whoselining 34 cooperates with the coupling member 20 as a main coupling oraxial disc clutch. Secured to the front end face 32 of the couplingmember 31 is a lining 33 which forms with the rear end face 60 of aclamping a member 39 a further axial disc clutch which is a controlcoupling via which the main coupling connected in series therewith maybe actuated. The two coupling linings comprise substantially differentdifferent mean diameters. This construction of the coupling member 31and provision of a control coupling and a main coupling is intended moreespecially to obtain a smooth jerk-free acceleration of the fan wheel onengaging. For this purpose, the coefficients of friction of -the linings33, 34 may advantageously be different, the coupling disc 34 preferablyhaving the greater coefficient. The coupling member 31 is mounted forrotation and axial displacement on the bushing 22 by means of a bearingbushing 36 of sintered metal advantageously secured to the inner wall 35of the coupling member 31. In the disengaged state of the frictioncoupling said member 31 is in the illustrated axial location in which itis not in contact with the coupling and clamping members 20, 39continuously driven by the journal 15.

The friction coupling also comprises a clamping mechanism 37 which is arotary friction locking mechanism and is illustrated in detail in FIGS.2 to 4. Said clamping mechanism comprises two clamping members coaxialwith the journal 15, namely a first clamping member 38 and a secondclamping member 39, which are relatively rotatable and axiallydisplaceable. The clamping member 39 forms at the same time a couplingmember of the control coupling. This clamping mechanism is illustratedin detail in FIGS. 2 and 4. The first clamping member 38 is pressed inthe direction of the arrow B towards the wax thermostat 24 by means of aspring 40 bearing on the free end face of the journal 15, the rear endface of the casing 25 of said wax thermostat forming a stop for theaxial end position of said clamping member. Said first clamping member38 further comprises a central cylindrical inner recess 41 in which isarranged a spring 42 which bears on the one hand on the first clampingmember 38 and on the other hand on the end face of the ram 30. Saidspring 42 is so rigid that on normal axial movement of the ram 30 itcannot be further compressed. Its purpose is rather that of an overloadprotection when in the engaged state of the friction coupling the ram 30tends to move further to the left due to increasing temperature of thewax 27. Consequently, in the normal case the spring 42 represents arigid connection between the ram 30 and the firs clamping member 38, aspring ring 43 being fitted in the upper edge of the recess 41 to engagebehind the collar 44 of the ram 30 and to effect that when the ram 30moves in the direction of the arrow C the first clamping member 38 isconstrained to move therewith.

The first clamping member comprises two radial diametrically oppositepins 45 and 46 which project with slight clearance through longitudinalslots 47 and 48 in the bushing 22. Secured to the pins 45 and 46 aresprings 50 and 51 which cooperate with the cylindrical outer wall 52 ofthe second clamping member 39 and form a freewheel clutch for the fanwheel. This clutch ensures that in the engaged state of the frictioncoupling the fan wheel is prevented from running faster than its drivespeed. This achieves a smooth running of the fan on rapid speedfluctuations of the engine.

The second clamping member is biased in the axial direction by means ofa pressure spring 54 bearing against a ring 53 let into the wall of thebushing 22 and is thereby constantly pressed against the pins 45, 46 ofthe first clamping member. Disposed on the radial end wall 55 of thesecond clamping member 39 are two diametrically opposite clamping cams56, 57 (FIGS. 24) whose ramp-shaped guide surfaces 58, 59 inclined at anangle a (FIG. 3) to the wall 55 form inclined planes and cooperate withthe pins 45, 46 to produce the pressure necessary from the firstcoupling state onwards. The height of these cams 56, 57 determines theposition of the second coupling state at which the friction coupling isautomatically disengaged.

The mode of operation of this regulating fan is as follows. As long asthe temperature to be controlled of the cooling air impinging on the waxthermostat 24 does not exceed a predetermined upper limit, the fan is inthe disengaged state illustrated in FIG. 1 so that the fan wheel 10 isnot driven by the journal constantly driven by the vehicle engine.

The pressure of the spring 54 holds the rotary clamping mechanism 37 ina disengaged position, as is illustrated in FIG.

2 or 4, in which it exerts no clamping pressure and thus produces noaxial coupling pressure. Such a position is also indicated in FIG. 3 inthe developed view a. FIG. 3 shows four relative positions of the endwall 55 of the second clamping member 39 and of the pins 45, 46 of thefirst clamping member. As mentioned, the position illustrated in thedevelopment a of the rotary clamping mechanism is its normal position inthe disengaged state. The pins then lie on the base sections 62, 63 withtheir lower surface, which is slightly curved a.

When the temperature to be controlled exceeds a value at which anadditional cooling by the fan wheel is necessary to avoid overheating ofthe internal combustion engine, the ram 30 moves as a result of theincreased temperature in the direction of the arrow D to the left anddisplaces the clamping mechanism 37 as a whole axially in the samedirection, thus changing the coupling state of the friction coupling.Since the first clamping member 38 of the clamping mechanism 37 isnonrotatably connected to the rotating journal 15 and drives the secondclamping member 39, a drive torque is exerted on the coupling member 31as soon as the coupling face 60 of the coupling member 31 as soon as thecoupling face 60 of the second clamping member 39 is pressed by thepressure of the ram 30 of the wax thermostat against the lining 33 ofthe coupling member 31 (first coupling state). Following this firstcoupling state the fan wheel It) begins to rotate and the torquetransmitted for this purpose by the friction coupling pivots the secondclamping member 39 of the clamping mechanism relatively to the clampingmember 38 into a position in which the pins 45, 46 run onto the inclinedguide surfaces 58, 59 of the cams 56, 57. The pins 45, 46 tend todisplace the second clamping member 39 axially in the direction of thearrow E (FIG. 3), thus increasing the coupling pressure exerted by thesecond clamping member. The inclination (angle a) of the guide surfaces58, 59 is such that following the first coupling state brought about bythe wax thermostat the clamping pressure until the main coupling isfully engaged without slip, i.e. until the coupling lining 34 bearsagainst the opposing face 64 of the coupling member 20 with a pressuresufficient to ensure the slip-free entraining of the fan wheel 10. As isthe disengaged state, this engaged state is a stable coupling statebecause the coupling pressure exerted by the clamping mechanism cannotcease spontaneously. The clamping mechanism is then in the positionshown in FIG. 3b. The cooling action of the fan wheel thereafter reducesthe coolant temperature and thus the temperature of the air acting onthe wax thermostat 24. As a result the ram 30 of the wax thermostatcreeps back in the direction of the arrow C, the pins 45, 46 thus movingcorrespondingly slowly in the direction of the arrow F upwardly on theguide surfaces 58, 59 of the cams; as this happens, the full couplingpressure is maintained. As soon as the temperature of the cooling airhas dropped to a value at which the bottom surfaces of the pins 45, 46reach the upper edges 66, 67 (FIG. 4) of the cams (second couplingstate), they slide over the cams 56, 57 as indicated in FIG. 30. Thepressure of the spring 54 thereby causes the second clamping member toniove in the direction of the arrow G, thus moving the clampingmechanism into its position shown in FIG. 2; the coupling is disengagedagain, passing rapidly through the slip range. The first and secondclamping members pass through the intermediate position illustrated inFIG. 3d, again into a position as shown in FIG. 3a. Since the additionalcooling effect of the fan wheel 10 is now removed, the temperature ofthe cooling air impinging on the wax thermostat can rise again dependingon the driving conditions and the engine output of the vehicle and thesame control process may be repeated. This two-point control does notend until an additional cooling by the fan is no longer necessary.

The ram 30 of the wax thermostat forms an abutment which absorbs thecoupling pressure. To keep the necessary coupling pressure as small aspossible the mean diameter D of the lining 34 is made as large aspossible and preferably substantially larger than the effective diameterd of the clamping mechanism i.e. the diameter of the end wall 55 of thesecond clamping member 39. To ensure slip-free driving of the fan bladethe angle a (FIG. 3) of the guide surfaces 58. 59 of the earns 56, 57must not exceed a predetermined maximum value. If the friction betweenthe pins 45, 46 and the guide surfaces 58, 59 is negligible, tan a}LD/Cl is approximately true, where p. is the coefficient of frictionbetween the lining 34 and coupling face 64 and d, D the said diameters.

Furthermore, it can be seen that engaging of the friction clutch takesplace at a higher temperature of the cooling air than disengaging, sinceat the instant of the first coupling state the ram 30 is displacedfurther to the left than at the instant of the second coupling state inwhich the pins 45, 46 slide over the edges 58, 59 of the cams 56, 57.This is desirable to prevent too rapid repeated reversal of the engagingand disengaging operations. The magnitude of the temperature differenceof engaging and disengaging depends on the height h of the cam (FIG. 3).In the illustrated embodiment this is so chosen that said temperaturedifference is approximately 5 C.

The friction coupling illustrated is also more especially distinguishedby the fact that although on engaging the fan wheel accelerates andpasses rapidly through the slip range of the coupling to nonslip drive,this acceleration is smooth and jerk-free. The smooth start is furtherimproved by dividing the friction clutch into control and maincouplings. Although this division of the friction coupling isparticularly advantageous, it may nevertheless be dispensed with in manycases.

The regulating fan illustrated in FIGS. 7 to 9 comprises a bistableclutch which includes a main coupling 110 which is a band clutch, acontrol coupling 111 which is an axial disc clutch and a clampingmechanism 112 similar to the clamping mechanism according to FIGS. 1 to4. The clamping mechanism has two positions which determine the firstand second coupling states.

113 denotes a V-belt pulley which is fixedly mounted on a rotatablymounted journal 114 and driven by means of the V- blet (not shown) bythe vehicle engine. Also fixedly mounted on the journal 114 is a hollowshaft 115 whose end 116 is slotted. Fitted in the free slotted end is awax thermostat 119 on which acts the cooling air heated by the radiator(not shown) of the vehicle engine, said thermostat being held in placeby a locking washer 117. This wax thermostat comprises an axiallydisplaceable ram 121 which passes through the thermostat casing 120 andwhich can move in the axial direction in dependence upon the temperatureof the wax thermostat. The higher the temperature, the more the ramprojects from the casing. Guided for axial displacement in the slots 122of the end 116 are two axial diagonally opposed arms 124 of a U- shapedfirst clamping diagonally opposed arms 124 of a U- shaped first clampingmember 123 whose center web 125 is pressed constantly against the freeend face of the ram 121 by means of a conical spring 126 bearing on theend face of the journal 114, so that the clamping member participates inthe axial movements of the ram. As is particularly apparent from FIG. 9,the two axial arms 124 are bent outwardly to form lugs 129 whichcooperate in turn with a cam plate 130 of a second clamping member 131of the clamping mechanism, the latter member comprising two lugs 133bent out of the plane of the disc and having obliquely inclined camfaces 132 whose function will be described hereinafter.

The disc-shaped second clamping member 131 is pressed by a pressurespring 127 against the lugs 129 of the first clamping member. Thepressure spring 127 bears on a retaining ring 134 which is inserted intothe hollow shaft 115 and which secures the inner ring 135 of a bearing136 mounted on the hollow shaft. Also fixedly mounted on the hollowshaft 115 is a cup-shaped main coupling member 137 which carries acylindrical lining 139. The components 113, 115, 117, 119, 123, 126,134, 135 and 137 are nonrotatably connected to the journal 114. Thesecond clamping member 131 with the pressure spring 127 also constantlyparticipates in the rotation but can turn relative to the first clampingmember 123 and is also axially displaceable with respect thereto.

On the other hand, the components carried by the outer ring 140 of theball bearing do not rotate with the journal 114 in the disengaged stateof the main and control coupling. These are the drum 141 fixedlyarranged on the outer ring 140, the control coupling member 142 bearingon the surface of the drum via a washer 143 and a cup spring 144, anannular spring 145 disposed at the underside of the control couplingmember, a coupling band 147 secured to the inside of the outer casing146 of the drum 141, the other end of which band is engaged in the freeend 149 of the annular spring bent in the axial direction, and a fanwheel 151 shown in dot-dash line and secured to the outer flange of thedrum 141 by means of bolts which are not shown. These components arecoupled to the journal 114 only in the engaged state of the main andcontrol couplings (FIG. 8). The control coupling 111 consists of thesecond clamping member 131, the control coupling member 142, on theupper part of which is fixedly mounted an annular coupling lining 152,and of the annular spring 145 secured to the control coupling member at153. The band clutch consists of the drum 141, the band 147 and the maincoupling member 137.

The bentup lugs 154 of the drum engage with their inwardly bent freeends over the coupling bear 142 and in the disengaged state of thecontrol coupling (FIG. 7) the assembly consisting of the washer 143, thecup spring 144 and the control coupling member 142 is mounted withslight axial clearance between the bent ends of the lugs 154 and theupper end face of the drum 141, so that said assembly can turn withrespect to the drum. The control coupling member 142 comprises on itsouter surface three radial projections 155 which project radially beyondthe lugs 154 and thus enable an angular movement of about 100 of thecontrol coupling member 142 with respect to the drum 141. The annularspring145 ensures that in the disengaged state the lugs 154 bear in theposition shown in dot-dash line at 156 in FIG. 9 against the projections155. In this position the coupling band 147 is relaxed and in theposition shown in FIG. 7. The annular spring, whose end 149 can moveresiliently in the direction of the double arrow C (FIG. 9) ensures asmooth engaging of the band coupling. In the engaged state the lugs 154bear against the other sides of the projections 155, thus limiting theresilient bending of the annular spring 145 and therefore the controlforce exerted thereby on the coupling band 147. This ensures a smoothengagement of the band coupling.

FIG. 8 is an exploded view of the most important components of thebistable clutch illustrated in FIGS. 7 and 8; the journal and allcomponents not essential for the understanding of the invention, such aslocking washers, bolts and the like, have been omitted for clarity.

The mode of operation of this bistable clutch is as follows:

In FIG. 7 the bistable clutch is in its disengaged state. The ram 121 ofthe wax thermostat 119 projects slightly beyond the casing 120 so thatthe first clamping member 123 assumed the position illustrated. Thesecond clamping member 131 is pressed by means of the spring 127 againstthe lugs 129, only one of which can be seen. In the disengaged state thelugs 129 can bear only on the deepest portion of the cam disc 130 andnot on the inclined cam faces 132 and thus exert no clamping pressure.The control coupling member is in its highest position. The controlcoupling (axial clutch) and the band clutch are disengaged.

When the temperature of the wax thermostat 119 increases, the ram 121moves correspondingly to the right, causing the first and secondclamping members 123, 131 to be moved to the right of the same extent.Following this movement the bottom of the second clamping member 131comes into contact with the coupling lining 152, this corresponding tothe first coupling state. Since the second clamping member then rotateswith the journal, it engages the control coupling member 142, thus beingbraked and rotating relatively to the lugs 129 of the first clampingmember until said lugs run onto the cam faces 132 and thus increase theaxial pressure on the second clamping member, the latter being pressedagainst the lining 152 of the coupling member 142 (FIG. 8). The secondclamping member is pressed downwardly by the camming engagement of thelugs 129 with the inclined cam faces 132. 133 against the action of thecup spring 144 until stopped by a shoulder of the hollow shaft 115 whichdetermines the maximum application pressure of the coupling faces of thecontrol coupling 111 in conjunction with the cup spring 144, resultinginter alia in a smoother engagement. The control coupling member 142 ispivoted relatively to the drum 141 in the direction of the arrow A (FIG.9). The annular spring 145 which is engaged in the lug 157 of thecoupling band 147 by means of its bent end 149 participates in thisangular movement and thus resiliently tensions the band 147 so that saidband is pressed against the associated coupling lining 139. The couplingband engages the lining 139 over an arc of about 320. A slip-freeconnection is then established very rapidly between the band 147preferably consisting of metal and the friction lining 139. With thecontrol coupling engaged the coupling band is constantly tensioned bymeans of the clamping mechanism and the annular spring 145 since thedrum 141 tends to lag with respect to the driven coupling member 142 dueto the braking torque exerted on said drum by the fan wheel connectedthereto. The driven coupling lining 139 tends to engrain the band andamplifies the tension of the latter, thus resulting in a considerableincrease in the surface pressure of the band. The torque D exerted onthe end 157 of the band by the annular spring produces a frictionaltorque D, of the band coupling of D,=D (e el where ,a is the coefficientof friction and D the angle of contact. In this manner it is possiblewith a low coupling pressure of the control coupling and a low tensionof the annular spring to couple the drum 141 and the associated fanwheel without slippage to the coupling lining 139 and thus to the shaftjournal. From the first coupling state onwards the engagement takesplace automatically and is not influenced by the wax thermostat. Theengaged state of the band clutch is maintained as long as the lugs 129press against'the inclined surfaces of the cams 133.

When the fan wheel has been started up the increased air flow cools theradiator and the temperature of the cooling air impinging on the waxthermostat 119 also falls steadily, causing the ram 121 to move to theleft. The first clamping member 123 also moves to the left accordingly,i.e. the lugs 129 move upwardly on the cam faces 132. As this happens,the position illustrated in FIG. 8 of the second clamping member 131 ismaintained unchanged. When the lugs 129 reach the upper edges of theinclined planes 132, thus leaving the latter, the second coupling stateis reached and from this point onwards the disengaging proceedsautomatically. At this instant the second clamping member 131 is pressedto the left by the pressure spring 127 until the lugs 129 lie on thedeepest portion of the cam disc 130, i.e. no longer on the inclined camfaces. The clamping mechanism is thus released and the control couplingdisengaged, cf. FIG. 7, so that torque is no longer exerted by thesecond clamping member on the control coupling member and the annularspring can no longer tension the coupling band, the band clutch thusrapidly disengaging automatically.

1 claim:

1. In a fan arrangement for cooling an engine, the arrangement includinga rotatable fan wheel,

a drive member adapted to be rotated by said engine,

a clutch operatively interposed between said drive member and said wheelfor drivingly connecting said member to said wheel, and temperatureresponsive clutch-operating means including a movable actuating member,

a body of temperature sensitive material in thermal contact with ambientair and connected to said actuating member for moving the same inresponse to a change in the temperature of said air, and

motion-transmitting means connecting said actuating member to saidclutch for engaging and disengaging the clutch in response to movementof the actuating member, the motion-transmitting means including twoclamping members mounted for relative angular movement about an axismovement, a first one of said clamping members being connected to saidactuating member for movement thereby in the direction of said axis, andto said drive member for rotation thereby about said axis,

coupling means for connecting the second coupling member to said wheelin response to an axial movement of said second clamping member from afirst to a second position and for thereby displacing the two clampingmembers angularly relative to each other when the rotary speeds of saidfan wheel and of said drive member differ from a predeterminedrelationship, and

cam means interposed between said clamping members for further axiallymoving said second clamping member from said second position toward athird axial position away from said first position, and for therebyengaging said clutch in response to said angular displacing,

the improvement which comprises:

a. said cam means including a cam member on one of said clamping membershaving a first face sloping obliquely in a circumferential direction andaxially toward the other clamping member and a second cam face offsetfrom said first face in said circumferential direction and leading awayfrom said other clamping member;

b. the cam means further including cam follower means on said otherclamping member for engagement with said cam member; and

c. yieldably resilient means holding said cam follower means inconsecutive abutting engagement with said first and second faces duringangular movement of said clamping members relative to each other in onedirection, whereby said clamping members are moved apart and thereaftermoved toward each other during said angular movement in said onedirection.

2. In an arrangement as set forth in claim 1, said axis being the axisof rotation ofsaid drive member.

3. In an arrangement as set forth in claim 2, securing means securingsaid first clamping member against rotation relative to said drivemember while permitting axial movement of said clamping member.

4. In an arrangement as set forth in claim 3, means securing said firstclamping member to said actuating member for joint movement in thedirection of said axis.

5. In an arrangement as set forth in claim 4, said second clampingmember being rotatably and axially movably mounted on said drive member.

6. In an arrangement as set forth in claim 5, said cam means includingan additional cam member on said one clamping member and substantiallyindentical with said first-mentioned cam member, said cam members beingangularly distributed about said axis, said cam follower means includingtwo cam follower members on said other clamping member distributed aboutsaid axis for simultaneous engagement with said first faces of said axisfor simultaneous engagement with said first faces of said cam membersduring said angular movement of the clamping members in said onedirection, and for simultaneous engagement with said second faces.

7. A fan arrangement for cooling an engine by means of a stream of aircomprising, in combination:

a drive member having an axis;

b. means for rotating said member about said axis when said engineoperates;

c. a fan wheel;

d. a clutch having a driven portion secured to said drive member forjoint rotation and a driving portion secured to aid wheel for jointrotation with the wheel about said axis;

e. actuating means including an actuating member and temperatureresponsive means in thermal contact with said air operatively connectedto said actuating member for axially moving the same in response to achange in the temperature of said air; f. clamping means for engagingand disengaging said clutch,

said clamping means including 1. a first clamping member secured to saiddrive member for joint rotation and secured to said actuating member forjoint axial movement,

2. a second clamping member axially interposed between said firstclamping member and said driving portion, said second clamping memberbeing axially movable and rotatable about said axis,

3. cooperating cam means on said clamping members responsive to relativeangular displacement of the same in a predetermined circumferentialdirection for axially moving said second clamping member toward saiddriving portion and responsive to further relative angular displacementof said clamping members in said predetermined direction for releasingsaid second clamping member,

4. yieldably resilient means biasing said second clamping member axiallytoward contact with said first clamping member, and

5. coupling means on said second clamping member and said drivingportion engageable by axial movement of said second clamping member forimpeding relative rotation of said second clamping member and of saiddriving portion; and

g. motion-transmitting means responsive to the axial movement of saidclamping member toward said driving portion for engaging said members ofsaid clutch for joint rotation.

8. An arrangement as set forth in claim 7, wherein said actuating meansare mounted on said drive member for rotation therewith.

1. In a fan arrangement for cooling an engine, the arrangement includinga rotatable fan wheel, a drive member adapted to be rotated by saidengine, a clutch operatively interposed between said drive member andsaid wheel for drivingly connecting said member to said wheel, andtemperature responsive clutch-operating means including a movableactuating member, a body of temperature sensitive material in thermalcontact with ambient air and connected to said actuating member formoving the same in response to a change in the temperature of said air,and motion-transmitting means connecting said actuating member to saidclutch for engaging and disengaging the clutch in response to movementof the actuating member, the motiontransmitting means including twoclamping members mounted for relative angular movement about an axismovement, a first one of said clamping members being connected to saidactuating member for movement thereby in the direction of said axis, andto said drive member for rotation thereby about said axis, couplingmeans for connecting the second coupling member to said wheel inresponse to an axial movement of said second clamping member from afirst to a second position and for thereby displacing the two clampingmembers angularly relative to each other when the rotary speeds of saidfan wheel and of said drive member differ from a predeterminedrelationship, and cam means interposed between said clamping members forfurther axially moving said second clamping member from said secondposition toward a third axial position away from said first position,and for thereby engaging said clutch in response to said angulardisplacing, the improvement which comprises: a. said cam means includinga cam member on one of said clamping members having a first face slopingobliquely in a circumferential direction and axially toward the otherclamping member and a second cam face offset from said first face insaid circumferential direction and leading away from said other clampingmember; b. the cam means further including cam follower means on saidother clamping member for engagement with said cam member; and c.yieldably resilient means holding said cam follower means in consecutiveabutting engagement with said first and second faces during angularmovement of said clamping members relative to each other in onedirection, whereby said clamping members are moved apart and thereaftermoved toward each other during said angular movement in said onedirection.
 2. In an arrangement as set forth in claim 1, said axis beingthe axis of rotation of said drive member.
 2. a second clamping memberaxially interposed between said first clamping member and said drivingportion, said second clamping member being axially movable and rotatableabout said axis,
 3. In an arrangement as set forth in claim 2, securingmeans securing said first clamping member against rotation relative tosaid drive member while permitting axial movement of said clampingmember.
 3. cooperating cam means on said clamping members responsive torelative angular displacement of the same in a predeterminedcircumferential direction for axially moving said second clamping membertoward said driving portion and responsive to further relative angulardisplacement of said clamping members in said predetermined directionfor releasing said second clamping member,
 4. In an arrangement as setforth in claim 3, means securing said first clamping member to saidactuating member for joint movement in the direction of said axis. 4.yieldably resilient means biasing said second clamping member axiallytoward contact with said first clamping member, and
 5. coupling means onsaid second clamping member and said driving portion engageable by axialmovement of said second clamping member for impeding relative rotationof said second clamping member and of said driving portion; and g.motion-transmitting means responsive to the axial movement of saidclamping member toward said driving portion for engaging said members ofsaid clutch for joint rotation.
 5. In an arrangement as set forth inclaim 4, said second clamping member being rotatably and axially movablymounted on said drive member.
 6. In an arrangement as set forth in claim5, said cam means including an additional cam member on said oneclamping member and substantially indentical with said first-mentionedcam member, said cam members being angularly distributed about saidaxis, said cam follower means including two cam follower members on saidother clamping member distributed about said axis for simultaneousengagement with said first faces of said axis for simultaneousengagement with said first faces of said cam members during said angularmovement of the clamping members in said one direction, and forsimultaneous engagement with said second faces.
 7. A fan arrangement forcooling an engine by means of a stream of air comprising, incombination: a drive member having an axis; b. means for rotating saidmember about said axis when said engine operates; c. a fan wheel; d. aclutch having a driven portion secured to said drive member for jointrotation and a driving portion secured to aid wheel for joint rotationwith the wheel about said axis; e. actuating means including anactuating member and temperature responsive means in thermal contactwith said air operatively connected to said actuating member for axiallymoving the same in response to a change in the temperature of said air;f. clamping means for engaging and disengaging said clutch, saidclamping means including
 8. An arrangement as set forth in claim 7,wherein said actuating means are mounted on said drive member forrotation therewith.